Telephone system



IM 7% T A W H TELEPHONE SYSTEM Filed Aug. 25,; 1934 at J,

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L 2 T A H TELEPHONE SYST M Filed Aug. 1954 om NBN M T R Patented Mar. 31, 1936 hdidtt AT ET HQ TELEPHONE SYSTEM Application August 25,

1934, Serial No. 741,378

In Germany September 5, 1933 8 Claims.

In telephone systems with relay selectors in which incoming lines cross a plurality of outgoing lines of similar direction of traflic, the requirement is often set that, during a connection between an incoming and an outgoing line another incoming line is to be connected up to the portion of the outgoing line remaining in the exchange. This case occurs, for instance, more particularly in private branch exchange systems when it is a question of changing over a public exchange connection to a definite subscribers station. The public exchange line is in this case the outgoing line, and the subscribers line the incoming, and in the following description the public exchange line is also considered as an outgoing line when it is a question of a changeover of an incoming public exchange connection from the main station receiving the public exchange call to the wanted private branch station. Further, the connection of a subscribers line to an outgoing line is also then necessary when it is a question of setting up an enquiry connection.

The object of the invention, now, is to effect these necessary couplings, existing connections 5 being maintained, to a definite outgoing line, re-

ducing as much as possible the number of the numerical impulse receivers necessary for reaching the wanted line and the auxiliary devices initiating and efiect the coupling, and this is achieved in that, through the switching operation (key pressure) which initiates the connecting up of a speaking station to an existing connection (setting up of incoming public exchange connections, enquiry connections), switching means are influenced which bring a numerical impulse receiver over the outgoing line under the influence of the speaking station carrying out the switching operation, and prepare the coupling of the station accessible over the numerical impulse receiver to the seized outgoing line.

An embodiment of the invention is shown in the drawings 1 to 6. The invention is not limited to the embodiment. Only the switching details necessary for understanding the invention have been shown.

t is a question of a full automatic relay exchange having two public exchange lines and a house line. The public exchange lines have the symbol ALI and ALII, while the house line is designated by HL. The setting up of the connections takes place in employing relays. No rotary selectors, therefore, are used. The subscribers privileged in respect to public exchange calls possess stations having earthing keys, while the non-public exchange privileged stations have no earthing key. A main station with special service facilities exists for the connecting up of incoming public exchange traffic.

House trafiic takes place as follows: After removing the handset the subscriber selects the number of the wanted. speaking station, which is then automatically called. During the call the caller receives the free signal. As soon as the called party replies, the ringing current is interrupted, and the speaking connection established. If after the conclusion of the conversation both subscribers hang up the handset, the connection is released, and the connection assembly is free for further seizure. If the wanted subscriber is busy, or if the house junction line is not free, the calling party receives the busy signal.

It the main station has the intention of carrying on an internal conversation, then, in contradistinction to a normal speaking station, the main station must first press the house key. A house lamp at its service apparatus then lights; selection of the wanted subscribers station then takes place.

If a subscriber entitled to public exchange calls wanted a connection to a subscriber of the public exchange, he presses, after lifting off his handset, the earthing key at the station. He is thereby automatically connected to a free junction line to the public exchange, and the house assembly seized on lifting ofif the handset is, after switching through has taken place, again free. A public exchange line can be reached even when the house assembly is busy. After switching through to the public exchange, selection takes place in usual manner after waiting for the public exchange signal. If both public exchange lines are busy, the subscriber receives the busy signal during the duration of key pressure. During a public exchange conversation a supervisory lamp lights for the time being at the main station, which lamp is associated with the busy public exchange line. The stations non-provileged in respect to public exchange calls, since they have no earthing key, cannot reach the public exchange.

If the main station wishes to conduct a public exchange conversation, the station presses the key of a free public exchange junction line. It is thereby directly connected through to the public exchange. change signal, dialling of the public exchange subscriber can be begun. During the conversation the supervisory lamp of the used public exchange line lights up. If both public exchange lines are busy, the operator recognizes this by 5 After waiting for the public exthe lighting up of both supervisory lamps at her service station. If, nevertheless, she presses one of the public exchange keys, all speaking stations receive the ticking signal.

In calling up the exchange by a subscriber of the public exchange, the alarm bell of the service station rings, and at the same time the calling lamp of the public exchange line lights upon which the call is arriving. The operator of the main station presses the public exchange key in question, and is thereby enabled to take over directly the public exchange conversation.

If an internal speaking station of the exchange is desired by the public exchange subscriber, the operator, after taking the instructions, presses the connecting key and dials the wanted internal subscriber. The latter takes over the public exchange conversation by pressing the key, while the main station hangs up. If the wanted internal subscriber is carrying on at the moment in question an internal conversation, the operator, by pressing the listening-in key, can enter the circuit of the public exchange conversation and notify the wanted internal speaking station of the existing call.

The connection of the operator to the existing conversation is effected by free signals to the two speaking subscribers. There is similarly a free signal when the operator connects herself to an existing public exchange conversation.

If a public exchange conversation exists, and ii enquiry is to be held, the enquiry subscriber presses the earthing key of his station and dials the wanted subscriber. The public exchange loop is held during the internal conversation, but the public exchange subscriber cannot concurrently hear the enquiry conversation. After termination of the enquiry, either the subscriber called in enquiry can take over the conversation by key pressure (change-over), or the enquiring subscriber, by again pressing the key, switches himself back, on his part, to the public exchange line, and can thereupon continue the public exchange conversation. If, during a public exchange conversation, enquiry to the main station is necessary, the key is to be pressed, as previously, and the number of the main station to be dialled. At the service station the calling lamp of that public exchange line then flickers on which the enquiry takes place. The operator thereupon presses the key associated with this public exchange line, and can conduct the enquiry conversation. If she wishes to take over the public exchange conversation, she presses the connecting key located at her service station.

Two of the internal speaking stations are provided with night switching. If a public exchange call arrives at the main station and if it is not answered by the latter within a certain time, the call is automatically passed on to the night station. Passing on of the call can be effected in two ways:

(1) The call arriving on the public exchange line ALI is passed on to one night station, the call arriving on the second public exchange line being passed on to the second night station.

(2) The public exchange calls of both public exchange lines arrive on the same night station, and are only answered by the latter.

Changing over for these two kinds of trafiic takes place, as may be desired, at the distributor.

At night the public exchange calls pass directly to both night stations, by-passing the main station, since now the night switch of both public exchange lines is changed over. In the case of passing on the call, as also in the case of night switching, the call is answered merely by taking off the receiver and listening, i. e., without pressing the key.

In the following the individual circuits will be described:

The six figures of the drawings are to be so placed together that Figs. 1 and 2, Figs. 3 and 4, and. Figs. 5 and 6 lie side by side.

Fig. 1 shows the subscribers connections (the main station is arranged at the top on the left), the two public exchange lines ALI and ALII and the house line I-IL.

Fig. 2 shows the sets of coupling relays.

Figs. 3 and 5 show the devices for the two public exchange lines.

Fig. 4 shows the house selector HW, while Fig. 6 shows the enquiry selector RW and also the arrangements for giving signals.

A. House TRAFFlC (a) Trafiic of normal stations If a subscriber of the private branch exchange system, for instance, subscriber N2, wishes to set up a house connection, to line N3, for example, the following circuit is closed for relay R2 by removing the receiver: earth, battery, resistance BOWi, (Fig. 1) contacts I02, 2112, 3a2, winding I of relay X2, subscribers station N2, winding II of relay X2, contacts 4112, 5172, 602, 'Iw2, 81172, line I300 (Fig. 1 and Fig. 2), 91172, winding of the relay R2, line 24 (Figs. 2 and 4) contacts M9123, IIIJbes, IIIvI, I I211, earth. Relay R2 energizes in this circuit. Through closing of contact IITZ the following circuit is closed for the impulse relay J, Fig. 1: earth, battery, winding II of relay J, contact I Ir2, winding I of relay J, earth. The following circuit for guard relay CH and transfer relay C2 is closed over contact I27: earth, battery, winding of the relay CH, contact I27 (Fig. 4), line 22 (Fig. 4 and Fig. 2), winding of relay 02, contacts I3T2, MTI, IEch, earth. Relays C2 and CH energize. The calling line is connected up over contacts I602 and I102 to the house junction line HL. Since, through actuation of these two c2-contacts the circuit of relay R2 is opened, relay R2 falls away. The feeding relay J is now held over the subscribers loop and relays C2 and CH hold over the contact I802, line 23 (Figs. 2 and 4) and the resistance I9Wz to earth. Through contact I5ch earth is removed from the chain of r-contacts (contacts IATI, I3r2, etc.) in order to prevent the energization of further C- relays in the case of the existing house connection. The following circuit for release relay VI (Fig. 4) is closed over contact 282': earth, battery, resistance ZIWi, winding of relay VI, earth, so that the impulse contact Hz is bridged by the contact 25M, and the connect relay C2 and guard relay CH can continue to hold during the impulse transmission, over contacts I802. Over contact Z'I'IJI (Fig. 4) the energizing circuit for the series relay V2 as also the holding circuit for release relay VI is prepared. Further, through contact Z'I'vl the following circuit for the relay An of the house selector HW (Fig. 4) is closed: earth, battery, winding of relay An, contacts 22mm, 2122!, earth. The house selector is connected to earth over contact 29cm, while over contact 35cm the signalling circuit for the free signal or the busy signal is prepared.

Upon the return of the dial switch, the feeding relay J is left as often currentless as the sub scribers loop is broken by the dial switch. Upon the first falling away of relay J the relay V2 (Fig. 4) energizes, in the following circuit: earth,

battery, resistance ZiWi, contact287', winding-f relay V2, contact El ot, earth. The relays VI and V2 then hold in known manner during the impulse transmission, owing to delayed action in falling away, through short circuiting. The relay V3 is energized over contact 3002', in the following circuit: earth, battery, winding of relay V3, contacts can, 28am, Zlvl, earth. A circuit for the Winding I of relay III of the house selector" l-IW is closed over contact 3W3: earth, battery, winding I of relay IH, contacts 3W3, 32.72, 29cm, Zl'ul, earth.

Over contact 337' the following circuit for relay K is closed on the first deenergization of J: earth, battery, winding of relay K, contacts B ll, 35p, 832', 29cm, El ot, earth. Relay K energizes. Over contacts 36k and 437a the following circuit for Winding II of relay III-I is closed, relay IH having been operated: earth, battery, resistance 3lW2', contacts 38p, 36k, winding I of relay IIH, contacts ttlllh, lcvh, llVIIh, tZIXh, talc, 29cm, 2112i,

earth. The relay Il-I further holds over its own contact ltIH and its winding II.

When, after termination of the first impulse, the relay J again energizes, the relay L is energized over contact 57, which relay was hitherto short circuited by contacts 46k and 331'. The relay K continues to hold in the circuit of relay L through contact 337'. The relay L energizes the relay N over its contact 412, and the formercontinues to hold over its contact 32% as long as the selector remains seized. Over contact 4811., Fig. 6, the signalling chain .(relays Ol-O l) and the ringing relay are started.

If, upon a second impulse, the relay J is again currentless, relay K falls away, since, through changing over contact 331', its circuit is interrupted. Relay IH is also currentless through changing over contact 437s of relay K, and only the relays L and IIH continue to hold, relay L remaining energized over its winding I and con tacts ii -i1, 355p, 2532' and relay III-I over its contact hilIllt and its winding II and contacts EilIVh, szvrn, 53VIII7L, E lXh, itk, 29am, 21m, earth. Further, over the fallen-away contacts 36k and title and the now-actuated contact 55113, the relay IIIl-I is energized over its winding II.

Upon termination of the second impulses the relay J is again energized. Relay L is released at contact but relays IIH and IIIH continue to hold.

The foregoing switching operations are repeated in the transmission of further impulses, in such manner that the relays K and L are energized after odd impulses, and after even impulses the relays K and L have fallen away.

When the impulse transmission is now terminated at the end of the third impulse, the counting relay of the relay selector which corresponds to the number of impulses dialed (the relay HIH) is held energized for the time being over its II winding. In the relay selector there are also provided the relays IVI-I to XH, in addition to the relays IH to IIIH. When, after impulse transmission has taken place, the relay J again remains continuously energized, series relay V2 falls away with delayed action, and energizes the changeover relay P over its contact 66122. Relay V3 is also currentless through opening of contact The contact 38p opens the circuit for that counting relay which corresponds to an impulse transmission higher by one than Was dialled (for instance, in dialling the number 3 the relay IV-H has momentarily energized over a contact of relay IIII-I, but is now deprived of current through contact 3810).

The testing and first ringing are limited by the interval between the energization of relay P and the falling away of slow acting relay V3.

If the called subscribers line N3 is free, the relay Pl energizes over the ringing circuit (Fig. 1) earth, battery, resistance WW2, contacts G lcil, 62b3, $30.3, winding I of relay X 5, subscribers station N3, choke DTZ, winding II of relay X3, contacts fi led, 55173, 6803, that, 5811111 of relay IIIR of the enquiry selector RW, (Fig. 6) line it (Fig. 1 and Fig. 2), contacts titIIIh (Fig. 2) of relay IIII-I of the house selector, contacts H723, 12p, winding I of relay Pi, earth to the source of alternating current, Fig. 6. The circuit for relay Fr is closed over contact liipi Fig. 4). This relay holds over its contacts "Mfr at IEfr the free signal is now inductively connnunicated to the calling subscriber over the relay 5. The free signal is a rattling in rhythm with the ringing impulse. Upon energization of relay Pi the first ringing signal is directly communicated to to wanted subscriber.

Further ringing takes place in known after timer relay V3 restores: From the lnterrupted generator lead through winding I of r'ng cut-off relay Abl.

As soon as the called subscriber removes th handset, the ring-cut-off relay A a-i ze through the continuous current flowing over subscriber loop, in the following circuit (Fig. l) earth, battery, resistance GQWZ', contacts @5133, 62b3, 8M3, winding I of relay subscribefs loop, winding II of relay X3, contacts M413, @5793, 6603, 67103, GEIIIT, line til (Fig. 1 and Fig. 2), fiilIIIh, contacts 80113, 8H1", winding I of relay Abi, contact 82 (relay not shown), earth. Relay Ab l holds over its winding II and contact 88191. The operating contact 83am (Fig.4) closes a circuit for the transfer relay C3 associated with the subscriber N3. Relay C3 energizes over the changed-over selector contact 8521M, and corn tinues to hold over its contact At contacts 9b and 9E, C3, Fig. 1, relay C3 switches the 3 over to the house line HL. Through chan over of the contact 28am, the relay An of the house selector I-IW is without current. Through falling away of relay Ah the circuits or relays F r, K, L, P, and IIIhN are interrupted.

With switching through of the called subscriber the speaking condition is reached. Both subscribers receive feeding current over the relay J. During the conversation the following relays are energized: J, VI, Abl, CH and the relays C12 and C3 of the two speaking subscribers.

The connection is released as soon the two subscribers have replaced their handsets. The relay J is without current through opening of the two subscribers loops, and short circuits relay VI which falls away with delayed action and breaks the circuit of relays Abi, C2 C3 and CH, whereby these relays fall away. The normal state of rest is then i e-established.

If the called subscriber is busy, the relay 1?! in contradistinction to the above (the called sub-- scriber is free) does not energize, since the loop for the relay PI is interrupted through the changed-over contacts of one of the transfer re lays A3, B3, and C3. The relay Fr, therefore, also does not receive any current and the subscriber receives a busy signal inductively over,

contacts lfifr to the relay J. The calling subscriber thereupon replaces his receiver.

If the house line is busy, and a further subscriber takes off his handset to make a call, the latter similarly receives a busy signal. In the circuit of line relays R (R2, R3, etc.) direct earth is lacking. This is rather formed only over the buzzer relay Su, which possesses such a high resistance that the line relays R cannot energize. The relay Su, however, energizes and interrupts the circuit through its own contact Hisu. It falls away, therefore, and immediately reenergizes. The busy signal is generated through this periodical opening and closing of the circuit.

(b) Trafiic of the main station HSt with a normal station If the main station HSt wishes to set up a house connection, it removes the handset, whereby the relay HU (Fig. 2) is energized in the following circuit over the changed-over switchhook (shown in Fig. 2) earth, battery, winding of the slow-acting relay HU, hook switch HUm, earth. Then the house key HT at the station is pressed. The relay H is thereby energized in the following circuit: earth, battery, winding of relay H, key I-IT, key T2, key Tl, switchhook I-IUm, earth. The relay HE is energized over contact Iilflh. The relay H holds over contact lillhh, the relay H also, after releasing the key HT. Both relays then hold throughout the conversation. The house lamp BL is connected up over contact i 5272 during the entire duration of conversation. The service station is connected to conductors a and 2) (associated with the house junction line HL) over the contacts lMhh and lBBhh (Fig. 1), so that the relay RI can now energize in the following circuit over the closed subscribers loop: earth, battery, resistance BllWz', contact iEJlcl alead of the junction line of the main station ESL", contact 347th, subscribers station, contacts ltfihh, lilficl, l08Ih, winding of relay Rt, line 24 (Fig. 2 and Fig. 4), contacts [89123, lllbes, Hint, H211, earth. After operation of relay RE the same switching operations takes place as previously described in the case of trafiic at a house station. The relay J is connected up over contact l 25H, while the relay C! is caused to energize over contact H611. This relay holds over its contact fll'lcl. In the circuit of relay C the relay Ch again becomes effective. The relays Vi and V2 are brought into operation over the impulsing contact. Impulse transmission then takes place in similar manner and influences the house selector HW, as already previously described.

B. OUTGOING PUBLIC EXCHANGE TRAFFIC Assuming the subscriber N2 wishes to set up a public exchange connection, he presses his earthing key Te2 after or while removing the receiver. The relay X2, constructed as a difierential relay, thereby energizes, in the following circuit: earth, battery, resistance SllWi, contacts i023, 2212, 3a2, winding I of relay X2, key Te2, earth. Connecting up of the private branch station to a free public exchange line is initiated over the contacts of relay X2. For public exchange calls, relays Al-A i, Fig. 2, are associated with the public exchange line ALI, and relays BiB l are associated with the public exchange line ALII.

For the following explanations it will be assumed that the public exchange line ALI is already seized, but the public exchange line ALII is free. Therefore, the guard relay Sp! (Fig. 5) of this public exchange line is then energized, so that the relays A (Fig. 2) of the private branch station in question cannot be energized over the m-contacts. With the public exchange line ALI busy, the following circuit for the relay A2 is broken (Fig. 4.) through the contact l25spl: earth, battery, resistance I 26Wi, contacts l2'lm, I25spl, I28hl, (relay HI, see Fig. 5), l29eb, line I32 (Fig. 4, Fig. 2), contacts l3lt2, I32a2, winding of relay A2, contact I335c2, line I34 (Fig. 2, Fig. 4), contacts l35xa, I36e, 1319a, earth. The relay A2 cannot therefore energize. Through closing of contact [35132 the following circuit is closed for the relay B2 (Fig. 4): earth, battery, resistance I26Wi, contacts l2'lm, l36spl, I3'lsp2, I38h2, l39ea, line ME] (Fig. 4), line I40 (Fig.2), contacts MHZ, i i2b2, winding I of relay B2, contact @5102, line M3 (Fig. 2), line I43 (Fig. 4), contacts i l lacb, M562, M6gb, earth. The relay B2 energizes in this circuit to connect the calling private branch station NZ to the public exchange line ALII over contacts l5fib2, and l5lb2. At contacts M2192 and H0122, Fig. 2, relay B2 switches itself into a holding circuit which includes winding II of relay T2 and relay GB. Relay T2, at contacts M5152 and IMtZ opens points in the circuits through which relays A2 and B2 can energize to cause seizure of a main-exchange trunk line from the calling line N2, while relay GB, at its contact Mfigb, removes a shunt from around relay EB, permitting this relay to operate in series with relays B2, T2, and GB.

When line N2 is switched over from the house equipment at contacts 2 and 5 of relay B2, to the main-exchange line ALII, through contacts i59b2 and l5lb2, the local, house equipment is thereby freed and the line ALII seized. The feeding relay S2 of this line is energized in the following circuit: earth, battery, winding II of relay S2, contacts i56b2, 3a2, winding I of relay X2, subscribers loop, winding II of relay X2, contacts m2, lElbZ, winding I of relay S2, earth. Relay S2 bridges retard coil Dr2| across the outgoing conductors at contact l'MsZ. The associated release relay QZI, Fig. 5, energizes in the following circuit: earth, battery, resistance i53W2', winding of relay Q2 I, contact I52s2, earth. The circuit of the calling relay Ar2, Fig. 3, of the public exchange line ALII is broken through contact lfiiiqZi. The circuit for the relay $792 of the public exchange line ALZ is closed over contact HSQ ZI and resistance I62Wi. At the same time the supervisory lamp UlZ of the public exchange line ALII, in a circuit in parallel with the relay S192, lights up, since contact i53u2 is closed. Relay Sp2 guards by its contact l3'lsp2 (Fig. 4) the seized public exchange line against any further seizure, since the energizing circuit for the coupling relays B (Bl-B4) of the remaining subscribers is broken. The relay B2 (Fig. 2) holds over its contacts new, and thereby causes also the relay T2 and the relay GB to energize. The relay T2, through its contact l3it2, breaks a further point in the circuit of relay A2 of the first public exchange line, in order not to bring about also a seizure of the possibly free first public exchange line in the case of subsequent enquiry. Through changing over of contact Mfigb the short circuit for the relay EB is removed, so that this becomes energized. The relay Y2 (Fig. 5) is ener ized over its winding I over contact M722, 265d), and l'llqill. Relay Y2 at contact 2761 2, locks itself in series with the I winding of relay Z2, but relay Z2, being short-circuitedat E6561), does not respond at this time. The talking circuit over ALII is prepared at contacts i59y2 and [10312. The common relay E (Fig. 4)

is caused to energize over contacts lfileb and lttqtl.

If the key TeZ is now released, the difierential relay X2 restores. The circuit for the relays EB, B2, T2, and GB is interrupted through opening of contact l35x2 (Fig. 2). Relay EB, restores immediately, but slow-acting relays B2 and GB do not. At contact i iieb, relay EB completes a new holding circuit through contacts l62q2| and I 65:02 for relays 32, T2, and GB, at the same time permitting relay E to restore again. Through opening of contact itiieb, the short circuit for the winding I of relay Z2, Fig. 5, is removed, so that the relay Z2 is caused to energize in series with relay Y2, winding I. The relay Z2, through opening of contact lii'lzZ and closing of contact M5822, connects up its winding II and the winding II of relay Y2. The relays Y2 and Z2 hold during the duration of the public exchange connection.

The subscriber, after switching through to the public exchange, waits for the dial signal from the public exchange, and then begins with the selection of the wanted public exchange subscriber. Upon the first impulse, the relay S2 changes over its contacts. The short circuit for the series relay Q22 (Fig. is removed through contact l52s2, so that also this relay energizes (contact i'ilqtl is closed). Relays Q21 and Q22 hold during the impulse transmission. The public exchange line is broken backwards by the contacts lll2q22 and ll3q22, Fig. 3. At the same time, over contact Ii2q22 the choke DRZI which was connected up after changing over of contact M482 is short circuited for the purpose of satisfactory impulse transmission.

The public exchange loop is interrupted in rhythm with the interruptions of the loop pro duced by the dial switch, through contact IMsZ, so that the impulses to the public exchange are given. After dialling, the subscriber is called, and the calling subscriber receives from thepublic exchange, the public exchange subscriber being free, the free signal. If it happens, after dialling, that the wanted subscriber is busy (busy signal from the public exchange), the connection is released by hanging up.

When the called subscriber replies, conversation can be carried on. Feeding of the internal subscriber takes place over the relay S2. The following relays are energized during the public exchange conversation: S2, Fig. 3, Q21, S 02, Y2, and Z2, Fig 5, B2 and T2, Fig. 2, and GB, Fig. 4.

The connection is released through hanging up the handset by the private branch station. The feeding relay S2 thereby falls away, and through its intermediary the whole of the remaining relays.

If a private branch station desires to set up a public exchange connection and, if at this moment both public exchange lines are alreadybusy, the private branch station receives the busy signal as continuous hums during key pressure. Since the Sp-relays (Spl and SpZ) of both public exchange lines, as previously described, are energized, none of the A and B relays (Al to A4, Bl to BA) can operate, contacts [258101 and I3'lsp2 being open.

(b) Outgoing public exchange traffic of the main station with operators facilities After the removing of the handset at the main station the relay HU, Fig. 2, is energized through hcckswitch HUM, Fig. 2, as already described, and prepares the energizing circuit for the coupling relays Al, Bl, respectively, which relate the main station to the public exchange lines through its'contacts lflllhu, l8lhu, respectively.

The operator, in order to obtain a public exchange connection, presses the public exchange key associated with a free public exchange line, for instance, T! for public exchange line ALI, the relay Al thereby energizing through its II winding. At the same time the relay Yi (Fig. 5) is energized over its winding I, since the line I85 of Fig. 5 leads to the key Tl in Fig. 2. The relay Al, by means of its contacts Nita! and Iiilal, connects the service station to the public exchange line ALI. The feeding relay SI is energized over its windings I and II in known manner over the subscribers loop. The release relay Qi i, Fig. 5, of the public exchange line ALI is energized at contact l88s1. The resistance l89Wi is connected in the circuit of relay Qll. The relay Qll holds over its contact l9llqll. At contacts at Bilhu and 262ml, Fig. 2, a holding circuit for relay Al (winding I) is closed through contacts 655x11, cc, and qll.

The relays EU and Al hold during the duration of the connection. The relay Yl connects through the public exchange line by its contacts i9lyl and l92yl. The relay Si connects the loop relay Dr! I in the public exchange line by its contact l93si. The calling lamp AL! is connected up over contact 194a! (Fig. 5). After relay Q is energized, the supervisory lamp UL! lights, since contacts i95qll and ifiiiul are closed. Both lamps light during the entire duration of the public exchange conversation. The relay Spl, in the circuit of which is connected the resistance l9lWi, is similar energized over contact l95q| I. Through changing over its contact 12581)! (Fig. 4), the relay Spl guards the public exchange line ALI against a further seizure through one of the remaining private branch stations.

When the key Ti is again released, the until then short circuited relay Zi energizes over its winding I, opens its contact l99el, and closes its contact 2902!, and therefore a circuit for its winding II and the winding II of relay Yl. Both relays hold over contact ZUiyl.

Numerical selection and ringingof the public exchange subscriber takes place as already described. After removing the handset by the subscriber of the public exchange, conversation can be carried on. When, at'the conclusion of the conversation, the main station hangs up the handset, relays Si and EU are first of all without current and, through their intermediary, all remaining relays. The lamps ALI and UL! are .also extinguished.

G. INCOMING PUBLIC EXCHANGE TRAFFIC If the exchange is called by the public exchange, the calling relay of the public exchange line (Ari), .of the public exchange line ALI or Ar2 of the public exchange line ALII, concerned isenergized dependent upon the ringing current. The relay I-Ii of the public exchange line ALI is energized'over contact 220ml, or the relay H2 of the public exchange line ALII is'energized over contact 22 M02. The relay I-Il holds over its contact 222M and its winding II in the following circuit in which relay H3i also energizes: earth, battery, winding of relay I-I3I, winding II of relay I-Il, contacts 222M, 223ql l, earth. Relay H2 correspondingly holds over its contact 22471.2 and contact 225112, and causes relay H32 to energize. The thermo-relay Thl of the public exchange line ALI heats over contact 22271.1, and the thermo-relay Th2 of the public exchange line ALII over the contact 224%. The contacts ZZBwII and 22'lwl2 are still closed. The further connection of the ringing is prepared through the thermo-relay. At the service station (Fig. 2) the alarm bell sounds, which bell is connected to potential over contact 228713! and 2297132, respectively. Moreover, the calling lamps ALI and AL2 respectively are connected up over contacts 236h3l, 23lh32, respectively. The calling lamp of the public exchange line on which the call arrives is therefore caused to illuminate.

Upon the call from the public exchange, the main station removes the handset and presses the T-key of the public exchange line on which the call has taken place, i. e., the key TI or T2. The circuits are then set up as already described in the case of outgoing public exchange traffic. The relays Qi l, QZI, respectively, are energized over the S-relays (SI, S2, respectively) which have energized after closure of the loop, so that now the call-holding relays HE and I-I3I, or H2 and H32 respectively are without current. The calling lamps ALI, AL2 respectively further light up over the contacts lg lal, Milbl respectively. The red supervisory lamp also burns during the duration of the conversation, viz., dependent on the contacts Iil5qll, I6Iq2I respectively.

After energization of the Y-relay of the public exchange line in question (relays YI, Y2 respectively), the public exchange line is connected through to the main station, and conversation can be carried on. Release of the connection takes place as already previously described.

If the operator upon a call from the public exchange is carrying on an internal conversation, or a public exchange conversation on the second public exchange line, she is made aware of the call by the lighting up of the calling lamp of the first public exchange line. If she is carrying on a house conversation, she has the possibility of terminating this by hanging up the receiver and of taking over the public exchange conversation by pressing the public exchange key associated with the public exchange line in question. If, however, she is carrying on, for instance, a public exchange conversation on the first public exchange line upon the arrival of a call on the second public exchange line, she can either terminate the first public exchange conversation by hanging up the handset, and take over the second by pressing the other public exchange key, or she may press the second public exchange key without previous hanging up. The first public exchange conversation is thereby held (waiting condition) and the second public exchange conversation can be carried on. The waiting condition for the first subscriber is reached in the following manner.

Upon arrival of the second public exchange conversation on the second public exchange line, the operator presses the public exchange key T2. The relay BI is thereby energized. Since the relay AI is energized through the already existing public exchange conversation, a circuit is temporarily closed for the windings I of relays Ill and U2 over the contacts 2500M and 25IbI. The holding circuit of relay AI of the first public exchange line which was closed over contact 262a| is interrupted through contact 26 IuI, so that this relay falls away. The connection on the public exchange line ALI is held, after falling away of relay Al, over the new current path for the relay SI of the first public exchange line: earth, battery, resistance 252Wz', contacts 253uI, IBGaI, line 620 (Fig. l and Fig. 3), winding I of relay SI, earth. Since, therefore, the relay SI is further held, the connection of the first public exchange line does not release. After falling away of relay Al the relay UI (Fig. 2) holds further over its Winding II and its contact 2532M while the relay U2 again falls away. As the relay BI remains energized through the depressed public exchange key T2, the falling away contact 263% now closes the holding circuit for the relay BI, so that this relay also remains energized after release of the key T2. (Contact 264M is closed.)

Also responsive to the operation of key T2, relay Y2, Fig. 5, operates over conductor 2'! as hereinbefore described, with the result that relay Z2 operates also through contact ITIqZI of the energized release relay QZI, when the key T2 is released. The main station is now connected over contacts 25%! and 25%| to the second public exchange line ALII. The flickering relay Fl, Fig. 6, is then energized over contact 2561 and the supervisory lamp ULI of the public exchange line ALI and the line 25'! (Fig. 5 and 6) the lamp extinguishes due to the high resistance of this relay. The relay chain OI-O l is started over contact 258;I, in consequence of which the supervisory lamp again lights for a short period (the operations are not described in further detail here), and again extinguishes. A flickering of the red supervisory lamp ULI consequently occurs, whereby the waiting condition of the public exchange line concerned is indicated. The red supervisory lamp UL2 of the second public exchange line, however, lights up permanently.

D. CONNECTING UP THE PUBLIC EXCHANGE CON- VERSATION A public exchange conversation exists between the main station and a subscriber of the public exchange on the public exchange line ALII. If an internal subscriber of the exchange is wanted by the public exchange subscriber (subscriber N3, for example), the operator presses the connecting key VT (Fig. l) at her service station, the differential relay XB being thereby energized. (If the public exchange conversation were on the public exchange line ALI, the relay XA would be energized). Since, in the case assumed, the relay X3 is energized, it causes the relay EB, Fig. 4, to energize over contact 259mb (Fig. 2). Through changing over of the contact I66eb winding I of the relay Y2, Fig. 5, energized during the public exchange conversation is without current. Relay Z2, winding II holds (through H5822, I65eb, and IIIq2I) after relay Y2 opens the previous holding circuit at contact 2103 2. Winding II of relay Y has not sufiicient turns to maintain the relay operated, being composed of re sistance wire. When relay Y2 restores, the public exchange line is broken in a backward direction through the contacts I69y2 and I'IIlyZ. The public exchange loop is simultaneously held over the contact IGBqZI and contact 269 2.

When relay Y2 restores, it closes a circuit at contact 2181/2 for relay A1138, through contact I'IIq2I of the energized release relay QZI. Relay An3l), at contact 2'l2an39, places ground potential on conductors 295 of the enquiry selector RW, Fig. 6, thereby preparing the selector for operation.

When relay XB restores responsive to the release of the key VT at the main station, it permits relay EB, Fig. 4, to restore, whereupon relay Z2, Fig. 5, is restored at contact [6561).

When the subscriber at the main station, as the next step, dials the digit 3 to set the enquiry selector RW on the line of the desired local subscriber (substation N3) relay S2 of the trunk line ALII restores momentarily three times. Armature l52s2, Fig. 5, brings the short circuited series relay Q22 into circuit with the energized release relay Q2l, whereby relay Q22 responds to the first impulse and remains operated throughout the series of impulses. At the same time, armature 28%? is controlling the counting relays KR and LR, Fig. 6, through the shifted armature 2820m3ll.

When series relay Q22 responds to the first impulse, it completes a circuit for relay Qill, Fig. 5, at contact E'Mq'ifi, through Zltemtii and EliiWi, conductor 295 being grounded as above explained. Relay Qlib closes a circuit at Ethic/3t for winding I of the first counting reay IR, by way of iilitnr and conductor 2%. Relay IR, thereupon at 28thremoves the shunt from around win-ding I of relay IIR, at the same time preparing a locking circuit for its own II winding.

When armature 28ls2 is restored on the first impulse, winding I of the relay KR is connected up over contact 28ls2, in the following circuit: earth, battery, winding I of relay KR, contacts 28%", 283727", QSZanSt, 28ls2, and conductor 2% to earth. After changing over of contact 285161 and 29AM, since contact 28611" is closed (the winding II of relay IR remains connected up over this contact), the relay IIR energizes over its winding I in the following circuit: earth, battery, resistance ZlEWi, resistance ftlWi, contacts 288101, 285701, winding I of relay IIR, cont-acts 29tIIIr, ZEHVT, 292VII1, 293IXT, 29 1M, line 295, etc., earth.

When, upon termination of the first impulse, the relay S2 again energizes, the relay LR. is energized over its Winding II in series with wind ing I of KR (contact iiiiillcr is closed), and continues to hold over its winding I. The relay LR energizes the relay NR over its contact Emir and this holds over its contact seem, so long as the selector is seized. The signalling chain of the pole changers and the ringing device is started over a contact of the relay NR (this is not de scribed in further detail here). When, upon the second impulse, the relay S2 is again wi hout current, the relay KR falls away, since its circuit (winding I) is interrupted. Relay LR, however, continues to hold through 286311", 283130", 2Ei20m3ii, and the restored armature 28is2. The relay IR is also without curren Further, the relay HR is energized over its winding I over the fallen away contacts Edilkr and 285M. Upon termination of the second impulse the relay S2 again energizes relay KR, which in turn energizes relay IIIR. These switching operations repeat themselves in the transmission of further impulses in such manner that the relays KR and LR. are always energized after odd impulses and have fallen away after even impulses. When the impulse transmission is terminated, the relay of the relay selector which corresponds to the number of impulses (i. e., in selecting the number the relay IIIR) is energized for the time being. Upon the termination of impulse transmision, the relay Q22, Fig. 5, falls away with delayed action and energizes the relay PR. The slow-acting relay QM is also without current (the further operations as already described in connection with the house selector HW).

Testing and the first ring are limited by the time interval between the energization of relay PR and the falling away of relay Q36.

If the subscriber is free, the relay Pl (Fig. 1, bottom right) energizes over the ringing circuit. The subscriber N3 has been dialled through selection of the digit 3; there thus arises for the winding II of relay Pi (Fig. 1) the following circuit; earth, battery, resistance GiiWz' (Fig. 1) contacts that, 52b3, 630$, winding I of the relay X3, subscribers station N3, choke DrZ, winding II of relay X3, contacts teat, 65b3, 6603, time, tiiIIIr, 333IIIT3, 33lq3fi, 332m, winding II of relay Pi, earth to the source of alterating current. Through contact 3337)! a circuit is closed for the relay FRR, Fig. 6. This relay energizes and holds over its contact ts lfrr. The free signal is now inductively transmitted over the relay J to the calling subscriber. Upon energize-tion of relay Pi, the first ring goes to the wanted subscriber, as already described. Further ringing similiarly takes place in the manner already described.

As soon as the called subscriber removes the handset the ring-cut-off relay Abl energizes over its winding III, Fig. 1, as contact Might has then again fallen away, and the contact ii 'iflfrr has energized. Earth is connected to the line (Fig. 4, Fig. 2) over contact Mich! (Fig. l). The windings II of relays B are connected in this line. Since, in the present case, the relay A1232, Fig. 5, of the public exchange junction line ALII is energized, the contact ii itcmeil (Fig. 2) is ciosed, and has connected battery over the resistance tell/Vi. Since in calling the subscriber N3 the relay IIIR of the enquiry selector RW is energized, the contact SMIIIT is closed, and contact SAEIIIT opened. Through opening of the contact 345KB" the short-circuit over the winding II of relay B55 is removed, so that this relay energizes. The relay A3 cannot energize over its winding II, since the contact 3 56111139 is opened. Through energization of relay B3 the called subscriber is connected over the closed contacts 321 223 and to the public exchange line ALIII on which the conversation lies.

After the main station has informed the internal subscriber that he is wanted by the public exchange, the subscriber at station N3, in order to reconnect the two separated sections of the trunk line ALII at the trunk-relay equipment 01 Fig. 3, presses the earthing key 'I'e3 located at his station, whereby his relay X3 is energized. The relay Eb is caused to energize over contact 35fia33, while the relay B3 continues to hold. The circuit of relay Bl of the main station is broken over contact i6 leb (Fig. 4) so that the main station is disconnected fromv the public exchange I line. The calling lamp in the service station extinguishes whereupon the operator hangs up the handset. The relays Y2 and Z2 reenergize over contact ifilleb, so that the public exchange line is now again connected through. The subscribers station is now connected with the public exchange subscriber. As already previously de scribed, the public exchange line used is also here guarded against further seizure.

Upon the initiation of an enquiry connection, therefore, (in this case it is a question or" the connection of a public exchange conversation) switching means (Antfi, Fig. 5) become effective which bring a numerical impulse receiver (RW) over the outgoing line under the influence of the speaking station holding enquiry, and prepare the coupling (over relays A or B) of the subscribers accessible over the numerical impulse receiver to the outgoing line seized by the station holding enquiry.

The contacts 3 l3a1i3ll or 346M130, Fig. 2, therefore, distinguish whether the coupling relay (A3) associated with the public exchange line ALI, or the coupling relay (B3) associated with the other public exchange line, shall become effective.

If more than two public exchange lines exist, the distinction between the coupling relays could not be effected over one relay (A1138), but the coupling relays of the An-relay associated with the public exchange line concerned from time to time must be brought into effect.

The coupling relays A4, B4 and C4 are associated with the subscriber N l, not shown.

If it is found, after dialling the private branch station by the main station, that the former is engaged on an internal conversation, the main station receives in known manner the busy signal. The main station has, however, the possibility of switching itself on to the existing house conversation by pressing the key MT. This takes place as follows: through dialling the internal subscriber called in the connecting operation the pole changer PW and the relay RF, Fig. 6, were started through the relay NR. Also the short circuit for the winding I of the relay M3 and for winding II of the relay B3, Fig. 2, of the called subscribers was removed in consequence of the opening of the selector contact concerned. (The relays M2 and M4 are associated with the other subscribers). The relays M2, M3 and M4 have also a winding II. If, now, the main station momentarily presses the listening-in key MT (Fig. l), high resistance relay Mh energizes and holds over its contact ENlmh and the line 3H (Fig, l and Fig. 2). The sensitive relay M3 in the circuit of the relay Mh further energizes over its winding I (but not the marginal relay B3), so that the public exchange junction line is connected up over the contacts 3121123 and 3131113 to the house junction line. The connecting-up signal is inductively transmitted to the house conectien over the induction winding of the relay S2.

At contacts 3l21n3 and 313m3, the main station is now connected to the engaged station N3. The main-station subscriber, therefore, can request the subscriber at N3 to clear out his local connection so as to receive the incoming call. As soon as the private branch station has hung up the receiver, it is automatically called, as listen-in relay Mb, Fig. 3, closes a circuit for the free relay FRR of selector RW, Fig. 6, at contact 11th.

The main station is disconnected from line ALII, as before described, when the subscriber at substation N3 replies.

Listen-in relay Mh, Fig. 4, restores, along with the other relays of the main station, when the receiver is replaced.

Even in the case that the internal subscriber is occupied with a public exchange call, the main station has the possibility of entering the circuit, viz.. by pressing the key MT. As already described, the relays M72 and the relay M3 energize, whereby the main station switches itself, over 1e contacts 3'i2m3 and 3131123, on to the private branch station and notifies it as to the existence of the public exchange call.

For the subscriber N3 the contacts 38Elm2 and ZB-lmi! correspond to the contacts 3121113 and iliimS.

E. ENQUIRY AND CHANGE-OVER (a) Enquiry of the main station An enquiry connection from the main station is set up in the same manner as if this station sets up a connection, which was already described. In this connection the essential feature was laid down that, in the enquiry, switching means which connect up the enquiry selector prepare the coupling of the subscriber with whom enquiry is to be held.

Upon termination of the enquiry, the main station takes over the public exchange call by again pressing the key VT. The relay XB is then reenergized, as already described. The relay EB energizes once more and closes the circuit for the fallen-away relay Y2, Fig, 5, over the contact l65eb. When the key is again released, the relay EB falls away. The relay Z2 energizes and relays Y2 and Z2 continue to hold over the contact 2'ifly2 (Fig. 3). By means of the relay Y2 the main station is switched back to the public exchange line. The private branch station reached in enquiry seizes the house assembly during pressure of the key of the main station, since the re lay B3 has fallen away. The station called in enquiry thereupon hangs up and the main station continues the public exchange conversation.

(b) Enquiry of normal subscribers station If one of the internal private branch stations, N2, for example, is carrying on a public exchange conversation, for instance, on the public exchange line ALI, and if enquiry is to be held to another private branch station, the earthing key T62, at the station is to be pressed. By so doing the differential relay X2 associated with the station energizes, energizing the relay EA (Fig. 4), since its short circuit is removed through the relay GA, already energized in the existing public exchange connection, through contact ifi'lga. The second public exchange line cannot be influenced upon pressing the key, since the circuit for relay EB is interrupted through the energized relay T of the first public exchange line over t-contacts. When the relay A2 (Fig. 2) of the subscriber N2 has energized, contact 599(12 has closed and the relay T2, winding I, has energized. The relay [13, upon energization, opens its contact lfitaE and closes its contact 402113, whereby the relay T3, winding I, energizes, while the relay AG opens its contact 403%, and closes its contact SS-de l, and in this case causes the relay T l, winding I, to energize. (The relays TZ-T4 also have each a winding II, which is connected up over contacts of the relays B).

Through opening of contacts seam, 4 i? or 42lt4, the circuit of the relay EB is broken for the time being, so that this relay cannot then energize.

As already previously described, the relay YL, Fig. 5, is without current owing to the energization of relay EA, so that the public exchange line is broken in a backward direction. The public exchange loop itself is further held. The selection of the internal subscriber now takes place in similar manner to that already described in the connection of a public exchange call through the main station. (Selection takes place over the enquiry selector RW with the assistance of relay Si The person speaking in enquiry therefore uses, for the enquiry conversation, the public exchange junction line concerned) The operations in ring-- ing, removing receiver and speaking are analogous to the operations already described in the setting up of a public exchange connection.

Upon conclusion of the enquiry conversation two cases may arise:

1. Ordinary enquiry, i. e., the first private branch station again takes over the public exchange call itself.

2. Changing over, i. e., the private branch exchange called in enquiry takes over the public exchange call. In the enquiry, the first private branch station, afterterrnination of the enquiry conversation, again presses its earthing key so that the relay EA energizes again and the relay Yl is reenergized. After releasing the key the relay Zl also energizes. The relay A of the second private branch station falls away through changing over of the ea-contact during key pressure of the first private branch station, so that the second private branch station is changed over to the house line. During the key pressure of the first private branch station, the second private branch station receives the busy signal in the house, since the relay R associated with the same cannot ene gize, due to the opened hes-contact. After receiving the busy signal the second private branch station hangs up. Through energization of relay YE the public exchange line is again connected through to the first private branch station, so that the first private branch station can again speak to the public exchange.

In changing-over the second private branch station takes over the public exchange conversation by key pressure. The operations are the same as those described above in the case of enquiry, with this difference, that the functions of both subscribers are interchanged, i. e., the second private branch station is connected to the public exchange over the public exchange line. while the first private branch station, upon pressure of the key of the second private branch station, receives busy signal in the house and hangs up.

If, during the public exchange conversation of a private branch station, an enquiry to the main station is necessary, the private branch station presses the earthing key and dials the main station. The signalling chain is started, and the calling lamp of the public exchange line concerned is caused to flicker dependent on the selector con tact (flickering relay Fl). The calling lamp lights dependent on the O relay of the signalling arrangement. The calling lamp flickers, therefore, dependent on the main station selected in the enquiry. Further, the public exchange alarm bell AW is caused to sound. The main station, in order to take over the enquiry conversation, presses the public exchange key of the public exchange line on which flickering is proceeding and thereby reaches, as already described previously, the public exchange line and can carry on the enquiry conversation. If the main station itself desires to take over the public exchange call upon termination of the enquiry, it presses the key VT, whereby the relay XA is energized and initiates the operation already described in preceding sections.

F. PASSING 0N CALLS AND NIGHT'SWITCHING If a public exchange call arrives at the main station and if it is not answered within a certain time (about seconds), the call is automatically passed on to the night station. By appropriate bridges at the distributor of the exchange it can be achieved that a call arriving on the public exchange line ALI is automatically passed on to the first night station (subscriber N4, not shown) and the call arriving on the second public exchange line to the second night station (subscriber N5, who is similarly not shown), or that the incoming calls on both public exchange lines are passed on only to one night station (subscriber N3).

The first class of further connection of the call will first be described. Dependent on the relays HI and 1-12 of the two public exchange lines .(Fig. 3) the thermoerelays Thl and Th2 are energized. If within a time of about 25 seconds the incoming call is not answered, these relays have so far heated up that relay Wil energizes through the relay Thl over contact 5B0th], and the relay W2! energizes over the contact 5Ulth2 of the relay Th2. The relays W II and W2l then hold over their own contacts 226w and 22'lwl2. The relay Wl l energizes over its contact 582ml 1 and relay WIZ in the following circuit: earth, battery, winding of the relay WIZ, contact 502wl l, choke Dr3l, contacts 563%, 5.9404, line 23 (Figs. 2 and i) resistance ISwi, earth.

The relay W2I connects up the relay W22 in the following circuit: earth, battery, winding of relay W22, contact 5Hlw2l, choke Dr-Zl, contacts 5Ht3, closed contact 8603, line 23 (Figs. 2 and 4;), earth. The relay Wl2 holds over its own contact 5|2w|2 and the relay W22 over its own contact 5131022. The ringing circuit to the night station N3 is closed over contact 61wl2, while the coupling relay of the public exchange line ALII is disconnected over contact 5l4wl2. The night station is then called, with the assistance of the signalling device which contains the relays (DI-O4, Simultaneously the white calling lamp at the main station lights up and similarly also the public exchange alarm bell AW sounds. When the night station removes the handset, the relays WA or WB previously slowly energized by alternating current energize over the continuous current now flowing in the subscribers loop, and the WA relay holds over its contact 5501000. The relay A3 oi the night station N 3 energizes over contact 55|wa (Fig. 2); the relay A3 then connects the night station to the public exchange junction line by means of its contacts 552a3 and 553113, so that the public exchange conversation can proceed.

The further connection of a call from public exchange calls on the second public exchange line to the second night station takes place in the same manner with the assistance of relay WB. The relay WB holds in this case over its contact 510201), and disconnection is efiected through the contact 554101).

The further connection of calls on both public exchange lines to the first night station (N3) is achieved by appropriate wiring at the distributor.

What is claimed is:

1. In an automatic telephone exchange, subscriber lines, trunk lines crossing each subscriber line, a connecting relay at the junction of each trunk line with a subscriber line, a dial-controlled automatic switch effective to select and operate any one of said relays, and means for associating said switch temporarily with any one of said trunk lines to enable it to be controlled thereover.

2. In an automatic telephone exchange, subscriber lines, trunk lines crossing each subscriber line, a connecting relay at the junction of each trunk line with a subscriber line, a dial-controlled automatic switch effective to select and operate any one of said relays, means for associating said switch temporarily with any one of said trunk lines to enable it to be controlled thereover, and means effective after said switch has been controlled over a trunk line to enable a selection to be made and a connection to be effected through the operation oi one of said connecting relays for destroying the temporary association between the trunk line and the switch, while leaving the effected connection between the trunk line and the selected subscriber line intact.

3. In a branch exchange trunk-connected with a main exchange, subscriber lines, a trunk line local to the branch exchange, a group of trunk lines extending from the branch exchange to the main exchange, means responsive to the removal of the receiver on a calling branch exchange line for connecting the associated line with said local trunk line provided the local trunk line is idle, a control key at the substation on the branch exchange line, and means responsive to an actuation of the said control key by the calling subscriber upon or subsequent to the removal of his receiver for transferring the connection from the said local trunk line to an idle one of the said inter-exchange trunk lines.

4. In an automatic branch exchange trunk-connected with a main exchange, means for interconnecting a local line in the branch exchange with one of the main-exchange trunk lines to permit an inter-exchange conversation, a selector common to the inter-exchange trunk lines, means controlled at will over the local line connected with an inter-exchange trunk line for bringing said selector under the control of the local line by way of the connected inter-exchange trunk line, means responsive to the dialling of the number assigned to another local line from the connected local line for operating said selector to bring the called local line into conversational connection with the dialling line by way of the trunk line and for signalling the subscriber on the called local line, whereby the two local sub- I scribers may converse with each other when the called subscriber removes his receiver, and means effective at the end of the ensuing conversation between the local subscribers and controllable from either local line for freeing the other local line and the said selector, leaving the unfreed local line in telephonic communication with the inter-exchange trunk line.

5. In an automatic branch exchange trunk connected with the main exchange, means effective when an inter-exchange connection is established and controllable at the will of the subscriber of the connected branch exchange line for temporarily severing the talking connection in the mainexchange line and for setting up an automatic connection between the branch-exchange end of the severed inter-exchange line and a desired other branch exchange line, and means controlled over the said other branch exchange line for reestablishing the temporarily severed main exchange connection and for freeing the first connected branch exchange line from the connection.

6. In an automatic branch exchange trunkconnected to a main exchange, local lines in the branch exchange including normal lines and a house line, inter-exchange trunks and a local trunk, push buttons at the substations on said lines, means operable dependent upon which button is pushed at the substation on the house line subsequent to the removal of the receiver for connecting the house line with the local trunk or with an idle one of the inter-exchange trunks, means responsive to the removal of the receiver at a substation on any one of the normal lines for connecting such line with the local trunk independent of push-button operation, and means responsive to the operation of the push button on the normal line accompanying the removal of the receiver for transferring the local line into connection with an idle inter-exchange trunk.

'7. In an automatic branch exchange trunk-connected with. a main exchange, local lines in the branch exchange, each of said lines having a substation thereon and a controlling push button at the substation, means normally responsive to the actuation of the push button at a substation accompanying the associated line with an idle inter-exchange trunk line pursuant to making an outgoing call to the main exchange, means controlled from an attendants station in the branch exchange for extending a connection to a desired local line pursuant to the completion of a connection incoming over a trunk line from the main exchange, and means effective under this condition responsive to the actuation of the controlling push button at the called local substation subsequent to the removal of the receiver for connecting the called local line with the specific trunk line over which the call for the local line has been received.

8. In an automatic branch exchange trunk-connected with a main exchange, a plurality of interexchange trunk lines, an inquiry selector for the common use of all said trunk lines, local lines in the branch exchange, a separate group of connecting relays assigned to each of the trunk lines for interconnecting such trunk line selectively with the local line, means for taking said inquiry selector for use from any one of the inter-exchange trunk lines and for operating it to select any desired one of the local lines, and means effective at the termination of the selection and dependent upon with which trunk line the inquiry selector is in association for operating the relay mechanism in the corresponding group to connect the trunk line with the selected local line.

HANS TATZL. 

